Vehicle antiskid braking system

ABSTRACT

This invention relates to an antiskid braking system for automotive vehicles, wherein the fluid supply connection provided between a variable fluid braking pressure control source and a set of fluid pressure actuated brake motors is controlled by fluid pressure modulating valve means actuated by output control signals generated by an antiskid unit in response to a skidding condition of the brake vehicle. The fluid supply connection is provided with a restricted area fluid passage disposed between said fluid source and said modulating valve means so as to substantially limit the fluid flow rate to said brake motors upon opening of said fluid supply connection, and thereby to dampen the build-up in pressure to the brake motors.

3,729,233 Apr. 24, 1973 VEHICLE ANTISKID BRAKING SYSTEM [75] Inventor:James Mangold, Tremblay-les Gonesse, France [73] Assignee: SocieteAnonyme D.B.A., South Bend, Ind.

[22] Filed: Mar. 10,1971

[21] AppL No.: 122,712

[30] Foreign Application Priority Data Mar. 12, 1970 France ..7008933[52] 1.1.8. Cl ..303/21 F, 188/181 A [51] Int. Cl. ..B60t 8/12 [58]Field of Search ..303/21 F, 21 CE, 303/21 CG, 61-63, 68-69, 6 C; 188/181[56] References Cited UNITED STATES PATENTS 3,550,966 12/1970 Leiber..303/21 F 3,574,416 4/1971 Skoyles ..303/21 F 3,494,670 2/1970 Leiber.......303/21 F FOREIGN PATENTS OR APPLICATIONS 1/1971 Germany ..303/21F7/1970 Germany ..303/21F Primary Examiner-Duane A. Reger Att0rneyW. N.Antonis and Flame, Hartz, Smith & Thompson 57] ABSTRACT This inventionrelates to an antiskid braking system for automotive vehicles, whereinthe fluid supply connection provided between a variable fluid brakingpressure control source and a set of fluid pressure actuated brakemotors is controlled by fluid pressure modulating valve means actuatedby output control signals generated by an antiskid unit in response to askidding condition of the brake vehicle. The fluid supply connection isprovided with a restricted area fluid passage disposed between saidfluid source and said modulating valve means so as to substantiallylimit the fluid flow rate to said brake motors upon opening of saidfluid supply connection, and thereby to dampen the build-up in pressureto the brake motors.

VEHICLE ANTISKID BRAKING SYSTEM This invention relates to an antiskidbraking system for automotive vehicles.

In the field of antiskid braking systems, it has already been proposedbraking systems of the type in which the fluid supply connectionprovided between a variable fluid braking pressure control source and aset of fluid pressure actuated brake motors relating to at least one ofthe wheels of the vehicle is controlled by fluid pressure modulatingvalve means which are adapted, when actuated by output control signalsgenerated by an antiskid control unit in response to a skiddingcondition of the braked vehicle, to terminate the said fluid supplyconnection and thereafter to connect said brake motors to a relativelylow fluid pressure reservoir for preventing the above braked vehiclewheel to be locked in rotation.

However, with such prior braking systems, it has been observed that uponheavy braking operations, the number of actuations of the pressuremodulating valve means as controlled by the antiskid control unit isvery large and thereby involves a great consumption of braking fluidfrom the pressure control source. Furthermore the relatively high rateof build-up in pressure to the brake motors whenever the valve means areactuated by the antiskid control unit to re-establish the fluid supplyconnection results in a sudden rise in braking torque and thereby in anunpleasant sensation for the passagers of the vehicle.

The main object of the above drawbacks.

According to the invention, there is provided an antiskid braking systemas defined hereinabove wherein a restricted area fluid passage isprovided in said fluid supply connection between said variable pressuresource and said pressure modulating valve means so as to substantiallylimit the fluid flow rate to said brake motors upon opening of saidfluid supply connection.

With such a feature, it will be understood that the location of therestricted passage in the supply connection results in a substantialdampening effects on the build-up in the braking pressure to the brakemotors and thereby in small rates of change in the braking effeet. Therestricted passage decreases the rate of change in the braking pressureto the brake motor and thereby the number of actuations of themodulating valve means.

According to a preferred embodiment of the invention, there is providedan anti-skid braking system as defined hereinabove whichfurthercomprises a by-pass fluid passage operatively provided inparallel fluid. flow relationship with said restricted area fluidpassage and controlled by a normally open by-pass valve means responsiveto and actuated by the differential fluid pressure across said pressuremodulating valve means for closing said by-pass passage whenever thesaid differential fluid pressure is above a predetermined value, as aresult of an effective actuation of the fluid pressure modulating valvemeans in response to said skidding condition of the vehicle. Such asecondary feature permits the braking pressure to by-pass the restrictedpassage and thus not to be subjected to the damping effect causedthereby upon a normal braking operation wherein the modulating valvemeansare not requested to modulate the braking pressure to the brakemotors.

invention is to avoid the One embodiment of the invention is describedhereinabove by way of example with reference to the accompanying drawingin which the single FIGURE is a schematic view of a hydraulic antiskidbraking system according to the invention.

When considering the braking system represented in the single FIGURE ofthe drawing, the reference numeral l0 designates a variable brakingpressure control source such as a conventional hydraulic mastercylinder, adapted to pressurize the hydraulic fluid from a reservoir 12as a function of the operation of an input brake control pedal 14.

The output orifice of the pressure control source 10 connected by afluid pressure supply connection 16 to two sets of fluid pressureactuated brake motors 18-19 and 22-23 of two pairs of wheels 20-21 and24-25 respectively relating to the front and the rear axles of a vehicle(not shown).

An electrically actuated shut-off valve 26 of any known type is locatedbetween the conduit 16 and the portion 28 thereof leading to the rearaxle wheel brake motors 22 and 23 so as to terminate the normal fluidcommunication between these motors and the control source 10. Anelectrically actuated normally closed exhaust valve 30 of any known typeis provided between the conduit 28 and an exhaust conduit 32 leading tothe reservoir 12. The electrovalves 26 and 30 are connected by wires 34and 36 respectively to the output terminals of an antiskid control unit38 responsive to the angular displacement of at least one of the rearaxle wheels 24 or 25 by means of an angular speed sensor 40 forinstance. The control unit 38 is of any known conventional type adaptedto generate electrical output control signal for actuating theelectrovalves 26 and 30 in response to predetermined skidding conditionsas sensed by the sensor 40 of the rear axle wheels upon an heavy brakingoperation of the vehicle.

According to the invention, a dampening device 44 is located in theconduit 16 between the output of the control source 10 and the input ofthe solenoid valve 26. The device 44 mainly comprises a restricted areafluid passage or orifice 46 adapted to substantially reduce theeffective flow area of the connection 16-28 and thereby the maximumpossible fluid flow therethrough under normal braking pressureconditions. A setting screw 48 may be operatively provided to permit thevarying of the effective fluid flow area of the orifice 46. The device44 is further provided with a by-pass fluid passage 50 located inparallel fluid flow relationship with the orifice 46. In the shownembodiment the said passage 50 is controlled by a by-pass valve 52defining therein two fluid chamber 51 and 53. Valve 52 is comprised of aspring loaded check valve which is normally urged in its open positionby a control piston 54, sealingly slidable in a bore 56 of the device44, and normally biased by a preloaded spring 58 in engagement with afixed abutment of the casing device 44. The piston 54 defines withinbore 56 two opposite fluid pressure chambers which are connected to theinput and the output of the electrovalve 26 respectively.

The operation of the braking system described hereinabove with respectto the rear axle wheels is as follows: In normal pressure releaseconditions, the shut-off valve 26 is open and the exhaust valve 30closed. Upon a normal braking actuation, the pressurized fluid flowcontrol source is supplied to rear brake motors 22 and 23 through supplyconnection l6, by-pass passage 50 and conduit 28 as long as theelectrovalve 26 remains in its normally open position and thereby doesnot cause any substantial differential pressure across the piston 54.

If it is assumed now that upon a relatively heavy braking actuation,certain skidding conditions are reached in that the rear axle wheels 24and/or 25 tend to lock, for instance, as a result of braking torqueapplied thereto becoming substantially higher than the maximum availablefriction torque. Upon this occurrence, the antiskid control unit 38 at afirst stage actuates the shut-off electrovalve 26 to its closed positionso as to terminate the fluid supply connection 16 between source 10 andbrake motors 22 and 23 and at a second stage actuates the exhaustelectrovalve 30 to its open position so as to connect the brake motors22 and 23 to the low fluid pressure reservoir 12. The resulting rapiddecrease of the pressure in the brake motors 22 and 23 permits thewheels 24 and 25 to be driven in rotation again. Once these latter havereached an angular speed substantially corresponding to the linear speedof the vehicle, the control unit 38 allows the solenoid valve 30 andthereafter the solenoid 26 to return to their normal respectivepositions so as to reestablish the supply connection between theconduits 16 and 28.

ln order to avoid a too rapid build-up in the pressure to the brakemotors 22 and 23, the dampening device 44 is provided. As a result ofthe above mentioned control unit operation, a substantial difference inpressure is produced across the valve 26 so that the valve 52 is biasedin its closed position by piston 54 thus closing the by-pass fluidpassage 50. The valve 52 is then maintained in its closed position bythe bias of the differential pressure of fluid contained in chambers 51and 53. Upon opening of the valve 26, the pressure fluid supplied by thesource 10 is directed to the brake motors 22 and 23 through the orifice46 so that the rate of the fluid flow to these motors as well as that ofthe pressure build-up is substantially reduced. It is to be noted thatdevice 44 does not introduce any time and/or dampening effects on thedecreased of the pressure in the conduit28 such as controlled either bythe exhaust solenoid valve 30 upon a skidding of the rear wheels or bythe release of the control on the brake pedal 14.

lf one considers the section of the braking system relative to the frontwheels 20 and 21 one notices that each of the brake motors 18 and 19 isconnected to the generaly supply conduit 16 by the intermediary of aconduit 60 or 61 and of a three-way electrovalve 62 or 63 connected bythe conductors 64 or 65 to an antiskid control block 66 or 67 sensitiveto the angular displacement of the corresponding wheel 20 or 21 by theintermediary for example of an angular speed detector 68 or 69. Eachelectrovalve 62 or 63 has a similar role to the unity of the twoelectrovalves 26 and 30 described above in order to reconnect theconduit 60 or 61 either to the supply conduit 16 or to the returnconduit 32 to the reservoir 12 according to the electric orders sent viathe conductors 64 or 65 by the antiskid control block 66 or 67.

A dampening device 70 substantially similar to the device 44 is placedin the section of the conduit 16 leading to the electrovalves 62 and 63.The device 70 is provided with an adjustable limited section orifice 72and a by-pass passage 74 placed parallel to said orifice 72. The by-passpassage 74 consists of two chambers 71 and 73 being in fluidcommunication through a channel in which is disposed a valve 76 normallyheld in its open position by a piston 78 charged by a reinforced spring80. Contrarily to the piston 54 of the device 44, the piston 78 is of atiered bore 82 in which it is slidingly placed and insulated, twocoaxial pressure chambers connected respectively to the conduits 60 and61 by the conduits 84 and 85. With such a device, the control of any oneof the electrovalves 62 or 63 by the corresponding antiskid controlblock brings on a fall in braking pressure in the corresponding brakeconduit 60 or 61 so that the piston 78 is applied towards the left ifone considers the drawing, by the pressure supplied by the source 10,which brings on the closure of bypass passage 74. Then, by the bias ofthe differential pressure of the fluid contained in chambers 71 and 73,acting on valve 76, the passage 74 is maintained closed. Thus in thecase of an unequal adherence of the two wheels 20 and 21 and of anautomatic control of the braking pressure sent to the brake motors ofthe wheel with the weakest adherence, for example the righand wheel 20,by the corresponding antiskid control block 66, the debit of fluid underpressure sent by the source 10 to the brake motors 19 becomessubstantially reduced by the actioning of the limited section orifice 72which thus substantially slows down the speed of the rise in pressure ofthe brake motor 19. With such a disposition, it will be understood thatthe appearance of a parasite torque produced on the steering of thevehicle by the difference between the braking torques used on the twosteering wheels such as wheels 20,21 will thus be dampened.

I claim: 1. In a vehicle antiskid braking system: operator-operatedfluid pressure generating means for generating braking pressure in saidsystem;

brake actuating means responsive to the fluid pressure generated by saidfluid pressure generating means for effecting a brake actuation;

means communicating the fluid pressure generating means with said brakeactuating means; and

means responsive to an incipient skidding condition of a vehicle wheeland generating an output signal in response thereto;

said communicating means including modulating means responsive to saidoutput signal for controlling fluid communication between said pressuregenerating means and said brake actuating means;

said communicating means including a restricted area passage to limitthe fluid flow rate to said actuating means, bypass passage means inparallel fluid flow relationship with said restricted area passage, andnormallyopen valve means in said bypass passage means normallypermitting uninhibited fluid communication therethrough, said valvemeans being responsive to the fluid pressure differential across saidmodulating means to close said valve means when said pressuredifferential attains a predetermined level.

2. The invention of claim 1:

said normally open valve means including a pressure differentialresponsive piston for operating said normally open valve means, andresilient means yieldably urging said piston toward a positionmaintaining said normally open valve means open,

said piston having a pair of opposed faces, one of said faces beingcommunicated to the fluid pressure on one side of said modulating means,the other face of said piston being communicated to the fluid pressureon the other side of said modulating means.

3. The invention of claim 1:

1. In a vehicle antiskid braking system: operator-operated fluidpressure generating means for generating braking pressure in saidsystem; brake actuating means responsive to the fluid pressure generatedby said fluid pressure generating means for effecting a brake actuation;means communicating the fluid pressure generating means with said brakeactuating means; and means responsive to an incipient skidding conditionof a vehicle wheel and generating an output signal in response thereto;said communicating means including modulating means responsive to saidoutput signal for controlling fluid communication between said pressuregenerating means and said brake actuating means; said communicatingmeans including a restricted area passage to limit the fluid flow rateto said actuating means, bypass passage means in parallel fluid flowrelationship with said restricted area passage, and normally open valvemeans in said bypass passage means normally permitting uninhibited fluidcommunication therethrough, said valve means being responsive to thefluid pressure differential across said modulating means to close saidvalve means when said pressure differential attains a predeterminedlevel.
 2. The invention of claim 1: said normally open valve meansincluding a pressure differential responsive piston for operating saidnormally open valve means, and resilient means yieldably urging saidpiston toward a position maintaining said normally open valve meansopen, said piston having a pair of opposed faces, one of said facesbeing communicated to the fluid pressure on one side of said modulatingmeans, the other face of said piston being communicated to the fluidpressure on the other side of said modulating means.
 3. The invention ofclaim 1: there being a pair of said brake actuating means, each of saidbrake actuating means actuating a corresponding brake; there being apair of said modulating means, one for each of said brake actuatingmeans; said normally open valve means including a valve operating pistonhaving a pair of opposed faces, said piston being controlled by thedifferential fluid pressures across both of the modulating means toclose said bypass passage means whenever one of said differential fluidpressures is above said predetermined level.